1. Field of the Invention
The present invention relates to binary digital image processing methods and more particularly to improved methods for enlarging binary image data stored in run representation form.
2. Description of the Prior Art
The following are systems representative of the prior art.
K. L. Anderson, F. C. Mintzer, and J. L. Mitchell, "Fast algorithm for enlarging an image by 1/5 in both dimensions," U.S. Pat. No. 4,569,081 teaches a method for expanding a binary image including the steps of: storing the image in bit sequence; inserting for each string of 5 bits along a first axis one or more expansion bits, to convert each said string of 5 bits to a string of 6 bits; assigning a value to each expansion bit generated by the above step; inserting one or more rows of expansion bits for each 5 rows of bits along a second axis of the image to convert each 5 rows of bits to 6 rows of bits along the second axis of the image; assigning a value to each expansion bit generated by the above steps; storing the enlarged image generated by the above steps.
Although the patent does deal with expansion of an image by a factor of 1.2, the patent does not expand an image in first and second dimensions by an integer factor by a method which operates on an image in run representation format as does the method according to the present invention. It operates on raster image data and examines only a small neighborhood surrounding each inserted pel to determine what the value of that pel should be, whereas the method according to the present invention can take into account pels over a larger area of the image when large features (straight lines, etc.) exist and can take steps to preserve and, if appropriate, smooth those features.
U.S. Pat. No. 4,303,948 describes an image enlargement process. The enlargement procedure differs from the method of the present invention in that it is a two-step process in which the image in bit map representation is first expanded by an integer factor and then reduced by a fractional factor. Expansion is accomplished by merely replicating bits, whereas the present invention modifies run representations for each run of each color in an image to be enlarged by an integer factor.
U.S. Pat. No. 4,254,409 describes an image enlargement process designed to do page composition using alphanumerics and simple graphics, rather than to operate on an already-composed image containing arbitrary data. It assumes that objects in the image are described as a series of graphics elements, each of which has a corresponding precanned precedure for enlarging it. It thus assumes some knowledge about what the image represents.
U.S. Pat. No. 4,409,591 is similar to 4,254,409. It operates only on a specified set of coded symbols (basically alphanumerics) rather than on arbitrary image data. Like 4,254,409, it assumes that the characters are described as a series of graphics elements; in this case enlargement is done by having precanned dot patterns available to create each element at any of a finite number of large sizes.
U.S. Pat. No. 4,367,533 describes enlargement of images by a process which appears to be replication of pixels, whereas the present invention modifies run representations for each run of each color in an image to be enlarged by an integer factor.
U.S. Pat. No. 4,357,604 describes a hardware method for enlarging the dot patterns corresponding to coded characters (not image data, although the image could be represented as coded data using a programmable symbol set) prior to display. Enlargement is by replicating pels in one dimension and by leaving extra space between pel columns in the other dimension.
U.S. Pat. No. 4,267,573 operates by transforming images (e.g. to a log spiral coordinate system). This is much more complex than the method of the present invention.
U.S. Pat. No. 4,153,896 scales the image first in one dimension and then in the other. This patent relies on hardware, that it describes, to read an image in either scan dimension. It is not appropriate for direct implementation in software, since most computers do not have this hardware capability. It is capable of scaling (enlarging or reducing) by an arbitrary factor. The enlargement algorithm is equivalent to replicating pels.
Although the prior art discussed above relates generally to the field of the present invention, none of the art teaches nor suggests the method of the present invention.